The present invention relates to an antenna device for a radio communications apparatus operating in at least two frequency bands, and comprising a helical first antenna element for the one frequency band, the helical antenna element having a supply end galvanically connected to the circuits of the radio communications apparatus, and a second, substantially rod-shaped antenna element for the second frequency band, the second antenna element being disposed along and outside the helical antenna element.
In radio communications apparatuses, in daily parlance mobile telephones, use is often made of different antennae for different operational states in the apparatus. In the standby state of the apparatus, paging mode, use is made of an antenna where one of the most important requirements is compact physical dimensions.
Mobile telephones operate within different frequency bands, for example approx. 450 MHz in the NMT band, approx. 900 MHz in the GSM band and approx. 1800 MHz in the DCS band. There are also mobile telephones in existence which are designed to be able to operate in more than one frequency band, and in such constructions antenna capacity is required in both of the frequency bands. Mobile telephones with three different frequency bands may also become topical.
Mobile telephones are previously known in the art possessing a plurality of antennae and in which the switching between these antennae takes place with the aid of mechanical switches. To employ switches in addition for switching between different frequency bands is hardly feasible in such small compact antenna which are employed in the standby state, the paging mode.
The present invention has for its object to design the antenna device intimated by way of introduction such that it may be produced with extremely compact dimensions and may be caused to operate in more than one frequency band without the employment of mechanical or other switches. The present invention further has for its object to design the antenna device in such a manner that it may be manufactured simply and economically at the same time as displaying good mechanical strength.
The objects forming the basis of the present invention will be attained if the antenna device intimated by way of introduction is characterized in that the rod-shaped antenna element has, in the region of the supply end of the helical antenna element, a supply portion which, at least partly and at a distance, surrounds the outer circumferential surface of the helical antenna element or its extension away from the helical antenna element.
Further advantages will be attained according to the present invention if the device according to the invention is also given one or more of the characterizing features as set forth in appended subclaims 2 to 7.